This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications No. 2000-349925, filed Nov. 16, 2000; and No. 2000-349926 filed Nov. 16, 2000, the entire contents of both of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a variable shape mirror and its manufacturing method, and more particularly to a small variable shape mirror applying the semiconductor technology and its manufacturing method, in a variable shape mirror capable of varying the curvature continuously.
2. Description of the Related Art
In a micro optical system applied in photo pickup or other micro optics, hitherto, for the purpose of simplifying the mechanism relating to focusing by using electromagnetic actuator, an ultrasmall variable focus mirror capable of varying the curvature of the reflection plane has been proposed.
In a small photographic optical system, application of variable focus mirror contributes to reduction of size.
Such variable focus mirror is expected to be manufactured at low cost and high precision by applying the so-called MEMS (Micro Electro-Mechanical System) based on the semiconductor manufacturing technology.
As an example of such technology, a reflecting mirror device as a variable focus mirror is disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2-101402.
The reflecting mirror device disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2-101402 is explained briefly by referring to FIGS. 8A and 8B, and FIGS. 9A to 9E.
FIGS. 8A and 8B are sectional view and perspective view showing the configuration of the reflecting mirror device of electrostatic attraction driving system disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2-101402.
In FIGS. 8A and 8B, reference numeral 11 is a glass or other insulating substrate (hereinafter called glass substrate), and a fixed side electrode layer 12 of conductive thin film is applied on the top of the glass substrate 11.
Reference numeral 13 is a silicon or other semiconductor substrate (hereinafter called silicon substrate), and a silicon dioxide thin film 14 is formed as a insulating film on a principal plane of the silicon substrate 13.
Reference numeral 15 is a vacancy formed on other principal plane in the central part of the silicon substrate 13, and this vacancy 15 is to set the central part of the silicon dioxide thin film 14 displaceably in the thickness direction.
Reference numeral 16 is a movable side electrode layer, and this variable side electrode layer 16 is laminated on the thin silicon dioxide film 14.
The central parts of the silicon dioxide thin film 14 and movable side electrode layer 16 form a reflecting mirror section 17.
The reflecting mirror section 17 is recessed and deformed to the fixed side electrode layer 12 side by the voltage applied both electrode layers of the fixed side electrode layer 12 and movable side electrode layer 16.
The silicon substrate 13 is bonded to the glass substrate 11 by way of a spacer member 18, with the silicon dioxide thin film 14 side downward.
Also, in FIGS. 8A and 8B, reference numeral 19 is a silicon dioxide thin film formed on other principal plane of the silicon substrate 13.
This reflecting mirror device is manufactured according to the manufacturing process diagrams shown in FIGS. 9A to 9E.
FIGS. 9A to 9E are sectional views for explaining the manufacturing process of the reflecting mirror device of electrostatic attraction driving system disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2-101402.
First, as shown in FIG. 9A, silicon dioxide thin films 19 and 14 of 400 to 500 nm in thickness are formed on both sides of a silicon substrate 13 of plane azimuth  less than 100 greater than  of which both sides are polished to mirror smoothness.
A gold thin film 16 of about 100 nm in thickness is applied on the silicon dioxide thin film 14 of the lower side.
Next, as shown in FIG. 9B, a photo resist 20 of specified pattern is applied on the silicon dioxide thin film 19, and a circular window opening 21 is formed by photolithography.
With the lower side of the substrate in protected state, a window is opened in the silicon dioxide thin film 14 by a hydrofluoric acid solution, using the photo resist 20 as mask.
Further, as shown in FIG. 9C, the silicon substrate 13 is immersed in an aqueous solution of ethylene diamine pyrocatechol, and the silicon substrate is etched from the area of the window opening 21.
At this time, as shown in the drawing, etching is stopped when the silicon dioxide 16 at the lower side is exposed.
Thus, a thin film of reflecting mirror section 17 composed of silicon dioxide film 14 and gold thin film 16 is left over.
On the other hand, in other process than mentioned above, as shown in FIG. 9D, a metal film of 100 nm in thickness is formed as a fixed side electrode layer 12 on the top of a glass substrate 11 of 300 nm in thickness.
Then, as shown in FIG. 9E, a silicon substrate 13 is adhered on the glass substrate 11 by way of a polyethylene spacer member 18 of about 100 xcexcm in thickness, so that a reflecting mirror device is manufactured as shown in FIGS. 8A and 8B.
This variable focus mirror manufactured by adhering substrates as disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2-101402 involves the following first and second problems when applied in the optical system where a high focusing performance is required such as a high definition camera.
The first problem is about the opening shape of the upper substrate on which the reflecting plane is formed.
That is, to form an opening, it is most preferable to etch by using an alkaline solution such as aqueous solution of ethylene diamine pyrocatechol mentioned above or potassium hydroxide from the viewpoint of cost and combination with thin film members.
By etching, however, due to crystal azimuth dependence of the silicon substrate, an accurate circular or elliptical opening shape cannot be obtained.
If the opening is square or polygonal, the deformation of the reflecting plane due to stress is asymmetrical, and the astigmatism increases, and the focusing performance is lowered.
The second problem is distortion of the upper substrate in the assembling process.
That is, the upper substrate is a single crystal silicon substrate, and a high mirror flatness is achieved, but when bonding with the lower substrate, or due to stress caused in the connection process for leading out the electrode of the upper substrate to the external lead, the upper substrate is slightly deformed, and an adverse effect is caused on the mirror focusing performance.
This problem may be somewhat avoided by keeping the junction position of the substrates or the connection position of the electrode of the upper substrate to the external part sufficiently away from the mirror opening area, but, as a result, the entire size of the mirror element is increased, which is contradictory to requirements of smaller size and lower cost of the optical system.
Incidentally, as the driving method of this kind of variable shape mirror, aside from the method of using electrostatic attraction force disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2-101402, a method of using piezoelectric effect disclosed in Jpn. Pat. Appln. KOKOKU Publication No. 3-81132, and a method of using fluid pressure disclosed in Jpn. Pat. Appln. KOKAI Publication No. 1-219801 are known.
These methods have their own merits and demerits, but the method of using fluid pressure is advantageous in an application where very high response is not required but a relatively large displacement is needed from the concave surface to the convex surface.
As an example of a variable shape mirror of such fluid pressure drive, the technique disclosed in Jpn. Pat. Appln. KOKAI Publication No. 1-219801 is briefly explained by referring to FIG. 10.
This variable focus mirror 1 is composed of a shell 2, chamber pressure adjusting device 3, and a reflecting mirror 4.
A pressure chamber 5 is formed in the shell 2, and a holder 7 for holding the reflecting mirror 4 airtight by O-rings 6 is formed in its opening.
In the pressure chamber 5, a pressure gauge 8 and a piping 9 of the chamber pressure adjusting device 3 are connected.
The piping 9 is composed of a compressor piping system 9a and a vacuum pump piping system 9b, and which are changed over appropriately between a compressor 21a and a vacuum pump 21b by means of electromagnetic operation valves 10a, 10b. 
To change over, the electromagnetic operation valves 10a, 10b are opened or closed by a controller 22.
The reflecting mirror 4 is made of a thin plate, and its reflecting plane 23 is coated with a reflecting material such as aluminum.
In the variable focus mirror 1 having such configuration, to form a concave reflecting plane 23a, the controller 22 is operated to close the electromagnetic operation valve 10a and open the electromagnetic operation valve 10b. 
As a result, the pressure chamber 5 communicates with the vacuum pump piping system 9b, and is evacuated to a negative pressure by the vacuum pump 21b. 
In this state, therefore, the reflecting mirror 4 is deflected to the side of the pressure chamber 5, and a concave reflecting plane 23a is formed.
On the other hand, to form a convex reflecting plane 23b, the controller 22 is operated to open the electromagnetic operation valve 10a and close the electromagnetic operation valve 10b. 
As a result, the pressure chamber 5 communicates with the compressor piping system 9a, and is compressed to a positive pressure by the compressor 21a. 
In this state, therefore, the reflecting mirror 4 is deflected to the opposite side of the pressure chamber 5, and a convex reflecting plane 23b is formed.
Further, by controlling the pressure in the pressure chamber 5 to be equal to the atmospheric pressure, the reflecting plane 23 maintains a flat reflecting plane 23c by its own elasticity.
The shape of the reflecting plane 23 can be varied by controlling the operation of the controller 22 according to the measurement of the pressure gauge 8, and the reflecting mirror 4 can be continuously set to an arbitrary focal length.
The variable shape mirror using such fluid pressure as driving source is particularly suitable to the application where change of focal distance in a wide range is required, as compared with the electrostatic attraction driving system in which the displacement is limited by the distance between electrodes or the piezoelectric driving system which is difficult to give a large deflection due to limit in the material of the reflecting plane.
The problem of the variable shape mirror using such fluid pressure as driving source is that it is difficult to reduce in size because pump or compressor is needed.
However, owing to the recent progress in micro machine technology, ultrasmall pumps applying the semiconductor manufacturing technology have been developed, and by using them, it is expected to realize a variable shape mirror of fluid pressure type to be assembled in a small device.
Nevertheless, the ultrasmall pump formed by the micro machine technology, generally, cannot generate a large pressure difference in a short time, and it is required to form the thin film as the reflecting plane by using a material of a very small rigidity, so that a large displacement may be obtained by a small pressure difference.
In this case, for precise control of displacement, pressure measurement of a very high resolution is needed, but if a pressure measuring instrument having such high precision, a third problem is caused, that is, the size cannot be reduced and the cost is increased.
In the light of the first and second problems, it is hence an object of the invention to present a variable shape mirror of small size and low cost capable of obtaining a high focusing performance, and its manufacturing method.
Other object of the invention is devised in the light of the third problem, and is intended to present a variable shape mirror having a displacement measuring function of small size and low cost.
To achieve the objects, according to the present invention, there is provided a variable shape mirror comprising:
a frame member having an opening; and
a thin film having a first region including a reflecting plane and a second region of higher rigidity than the first region disposed in the outer periphery of the first region, being supported in the opening of the frame member.
Also to achieve the objects, according to the present invention, there is provided a variable shape mirror comprising:
a frame member having a first opening and a second opening;
a first thin film having a reflecting plane, forming an electrode, and supported in the first opening of the frame member;
a second thin film forming an electrode electrically conducting with the electrode of the first thin film, and supported in the second opening of the frame member;
a substrate bonded to the frame member at a specified interval, and having an electrode at a position opposite to the electrode of the second thin film; and
a conductive protrusion disposed on the electrode of the second thin film or the electrode of the substrate, and having a height higher than the specified interval.
Also to achieve the objects, according to the present invention, according to the present invention, there is provided a variable shape mirror comprising:
a frame member having an opening;
a thin film having a reflecting plane supported in the opening of the frame member; and
a substrate bonded to the frame member at a specified interval by way of a spacer,
wherein the space between the portion of the frame member having the opening and the substrate is not closed.
Moreover, to achieve the objects, according to the present invention, there is provided a manufacturing method of variable shape mirror for bonding a frame member of reflecting plane side of variable shape and a substrate at a specified interval, comprising:
applying a photosensitive coating material on either the frame member or the substrate, exposing by using a specified mask, and developing to form a spacer; and
bonding the other one of the frame member or the substrate to the spacer, and heating to adhere together.
To achieve the objects, according to the present invention, there is provided a variable shape mirror comprising:
a thin film having a reflecting plane;
a member for supporting the thin film;
means which deforms the thin film; and
a sensor formed in part of the thin film for detecting the deformation of the thin film.
The sensor for detecting the deformation of the thin film is a distortion sensor formed on the outer circumference of the thin film.
The outer circumference is greater in film thickness as compared with the central part of the thin film.
Also to achieve the objects, according to the present invention, there is provided a variable shape mirror comprising:
a frame member having at least a first opening and a second opening;
a first thin film having a reflecting plane supported in the first opening of the frame member;
a second thin film supported in the second opening of the frame member;
means which deforms the first thin film and second thin film by applying an equal fluid pressure to the first thin film and second thin film; and
a sensor formed in part of the second thin film for detecting the deformation of the second thin film.
The frame member is mainly composed of single crystal silicon.
The second thin film has a protrusion projecting from the frame member made of a thin film of single crystal silicon, in the peripheral area of the second opening.
The sensor for detecting the deformation of the second thin film is formed on the protrusion.
Further, to achieve the objects, according to the present invention, there is provided a small variable shape mirror applying semiconductor technology comprising:
a frame member made of single crystal silicon having an opening;
a polyimide thin film having a reflecting plane for covering the opening;
means which deforms the thin film by applying a fluid pressure to the thin film; and
a distortion sensor for detecting the change of resistance value of resistance pattern formed on the thin film exposed to the fluid pressure.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.